1. Field of the Invention
The present invention relates to a superconductive apparatus, and more particularly to a superconductive apparatus comprising a superconductive device airtightly packaged, such as a superconductive magneto-resistive device to be used as a magnetic sensor.
2. Description of Related Art
Conventionally, a magnetic sensor utilizing a superconductive magneto-resistive device has been proposed. In the magnetic sensor, there are formed a pair of current electrodes and a pair of voltage electrodes thereon. A current is supplied to the magnetic sensor by an external power source through lead wires which are connected to a pair of current electrodes. A voltage generated between a pair of voltage electrodes is measured to detect a change in the resistance thereof when a magnetic field is applied thereto. Therefore, the above magnetic sensor can detect an extremely small magnetic field by measuring the above voltage. The magnetic sensor has been used such that the magneto-resistive device thereof is exposed to the outside.
Since this sort of superconductive apparatii have such advantages that they have a simple structure and a high reliability, and also the manufacturing method thereof is relatively simple, they have been widely used. However, when the superconductive apparatii receive a thermal cycle which changes from room temperature to a low temperature such as the threshold temperature of the superconductive magneto-resistive device and vice versa, drops of water adhere to the surface of the superconductive magneto-resistive device thereby causing the compounds of the material to change to the other compounds resulting in the superconductive property of the superconductive magneto-resistive device deteriorating.
Further, since the surface of the superconductive magneto-resistive device is exposed to the outside, it is necessary to handle it carefully.
Furthermore, since the magnetic sensitivity of the superconductive magneto-resistive device varies depending upon the temperature thereof, it is necessary to measure the temperature of the superconductive magneto-resistive device upon cooling it in order to correct the measurement result of the magnetic field according to the above temperature dependency.